To estimate a maximum purchase price for the coin in question, we can analyze the provided data and consider several factors:

1. Current asking price: 1400 euros.
2. Coin condition: 80 (MBC+), indicating good condition, although not the best.
3. Auction history:
- The coin has been auctioned 5 times in the past, of which it has sold 4 times.
- The average hammer price in previous auctions is 1402.75 euros.
- Previous hammer prices varied, with a maximum of 1900 euros and a minimum of 1000 euros.

4. Price trends:
- In the 2024 auction, the coin sold for 1510 euros with a condition of 80, similar to the current one.
- In the 2021 auction, with a condition of 70, it sold for 1201 euros.

Given that the current coin condition is 80, which is comparable to the 2024 auction, and considering that the highest hammer price in the past was 1900 euros, we can estimate a maximum purchase price.

Maximum purchase price estimate:
- Based on the highest hammer price (1900 euros) and the recent hammer price (1510 euros), a reasonable maximum price could be between 1600 and 1800 euros, considering that the condition is good but not excellent.

Therefore, an estimated maximum purchase price could be 1700 euros. This allows for a margin for competition in the auction and reflects the historical value of the coin.